The invention relates to an indicator dial comprising at least one scale which consists of marking symbols, and further comprising at least one indication area a translucent, illuminable indicator warning field, which is illuminable in the case of warning.
Known dials of this type consist usually of a thin sheet metal plate having a black coating on the side that faces the viewer, and a scale printed thereon with white and red symbols, and further provided, at one or more scale-free spots, with an indication area. Each indication area consists of a usually rectangular or arched recess or opening in the sheet metal plate, behind which recess a colored plastic material window is provided. Behind the plastic material window an incandescent lamp is arranged which, when it is switched on, illuminates the plastic material window and thus communicates to the viewer an optical signal indicating a proper or improper functioning of a physical force. For better distinction of the signals, the plastic material windows are usually provided with symbols or a lettering which are either permanently visible or become visible only when the light is switched on. In the last-mentioned case, the symbols or letters are located on the side of the plastic window that faces away from the viewer. The illumination of the entire dial surface, e.g. at darkness, takes place by the incident light process, i.e., the light of an incandescent lamp strikes the face of the dial directly or indirectly.
Furthermore, dials are also known that consist of a plate which is thick in comparison to the aforementioned dials, and which is made of transparent material. The plate is provided on both sides with a light-reflecting layer or coat, and the coat facing the viewer is made so thin that light can pass through it and emerge. This thin layer is covered with an opaque layer which is provided with interruptions that form marking symbols and scale marks. The layer on the side facing away from the viewer has an aperture through which light can be radiated into the interior of the plate so as to illuminate the dial. In these dials, illuminated according to the floodlight principle, provision of a recess for a separately illuminable indication area is not possible since the uniformity of the illumination of the dial would be disturbed by such recess, and undesirable illumination losses would also occur.